A number of diseases, illnesses and other medical conditions are treatable at least in part by dilatation of a bone, tissue or duct. For example, medical conditions and/or physical injuries can lead to or predispose a bone to deformity, such as a fracture. A familiar example is osteoporosis, in which bones lose calcium and break more easily. The human spinal column, comprised of interconnected vertebrae or vertebral bodies, has proven to be especially susceptible to the effects of osteoporosis. A vertebral body weakened by osteoporosis can fracture from a fall, or simply during routine activities. When a vertebral body fractures, it can collapse and change the shape of the spine. The damaged portion of the spine becomes shorter, and the rest of the spine above the broken vertebral body bends forward. As additional vertebral fractures occur, the spine shortens further, increasingly forcing the individual into a hunched-over posture.
As taught by U.S. Pat. No. 6,066,154 (Reiley et al.), which is incorporated herein by reference, it is known in the art to use an inflatable balloon-like device to treat certain bone conditions, resulting from osteoporosis, avascular necrosis, bone cancer and the like, that predispose a bone to, or lead to, fracture or collapse. A particularly common application is in the treatment of vertebral body compression fractures resulting from osteoporosis.
Typical treatment of such conditions includes a series of steps which a surgeon or health care provider can perform to form a cavity in an interior region of pathological bone, including but not limited to osteoporotic bone, osteoporotic fractured metaphyseal and epiphyseal bone, osteoporotic vertebral bodies, fractured osteoporotic vertebral bodies, fractures of vertebral bodies due to tumors especially round cell tumors, avascular necrosis of the epiphyses of long bones, especially avascular necrosis of the proximal femur, distal femur and proximal humerus and defects arising from endocrine conditions.
The method typically further includes the steps of making an incision in the skin (usually one incision, but a second small incision may also be required if a suction egress is used) followed by the placement of a guide pin which is passed through the soft tissue down to and into the bone.
The method of the Reiley '154 patent further includes the steps of drilling the bone to be treated to form a cavity or passage in the bone, following which an inflatable balloon-like device is inserted into the cavity or passage where it is inflated. The inflation of the inflatable device causes a compacting of the cancellous bone and bone marrow against the inner surface of the cortical wall of the bone to further enlarge the cavity or passage. The inflatable device is then deflated and then is completely removed from the bone. The art further teaches that a smaller inflatable device (a starter balloon) can be used initially, if needed, to initiate the compacting of the bone marrow and to commence the formation of the cavity or passage in the cancellous bone and marrow. After this has occurred, a larger, inflatable device can be inserted into the cavity or passage to further compact the bone marrow in all directions.
At this point in accordance with Reiley '154, a flowable biocompatible filling material, such as methylmethacrylate cement or a synthetic bone substitute, is directed into the bone cavity or passage that has been formed and enlarged, and the filling material is allowed to set to a hardened condition to provide ongoing structural support for the bone. Following this latter step, the insertion instruments are removed from the body and the incision in the skin is covered with a bandage.
A related U.S. Pat. No. 6,048,346 (Reiley et al.), which is also incorporated herein by reference, teaches an improved mechanical bone cement injection assembly, which is described as constituting an improvement over prior art devices that operated “similar to a household caulking gun” in that it facilitates greater control over the placement of cement and other flowable liquids into an interior region of a bone.
Another inflatable apparatus intended for deployment into interior body regions is described in U.S. Pat. No. 5,972,015 (Scribner et al.), which is also incorporated herein by reference. The Scribner '015 patent describes a catheter tube extending along a first axis in conjunction with an expandable structure having an expanded geometry oriented about a second axis, not aligned with the first axis, so as to treat an asymmetrically-shaped interior body region or where the access channel cannot be aligned with the body region to be treated. A particular application of this technology is stated to be for the fixation of fractures or other osteoporotic and non-osteoporotic conditions of human and animal bones, specifically for treating a human lumbar vertebra.
Two somewhat earlier patents describing similar apparatus and methods for treating vertebral body compression fractures and the like using an inflatable balloon-like element inserted into the bone cavity are U.S. Pat. Nos. 5,108,404 (Scholten et al.) and 4,969,888 (Scholten et al.), both of which are also incorporated herein by reference.
Numerous problems remain, however, with the prior art apparatuses and methods. For successful expansion of a fractured vertebral body, an expandable element inserted into the vertebral cavity must be capable of being inflated to a relatively large working diameter of about 12 mm-25 mm, starting with a relatively short balloon working length, e.g., about 12 mm-25 mm, sized to fit inside the vertebral cavity, at very high working pressures on the order of 200-400 psi or higher. It has been found that the use of lower inflation pressure in such applications results in only a partial, incomplete expansion of the fractured vertebral body. When that partially-expanded vertebral body is subsequently filled with cement or comparable material, which then hardens, there is a permanent remaining spinal deformity at that vertebral body. Not only must the expandable/inflatable element in the vertebral cavity be capable of inflation to very high pressure without potentially disastrous rupture in order to fully expand a collapsed/fractured vertebral body, in addition the inflated element must resist puncture by hard, sharp cancellous bone and surface irregularities around the outer edges of the vertebral cavity. Standard materials commonly used in the prior art for constructing the expandable, balloon-like element used to expand bone cavities cannot be safely inflated to very high pressures on the order of 200-400 psi or higher, and, when inflated, typically do not have a high degree of puncture resistance.
One possible approach to improve the strength of the balloon-like elements to make them better able to withstand very high inflation pressures would be to use thicker balloon walls and/or to make these elements out of stiffer, stronger materials. There are several reasons, however, why these seemingly straightforward solutions have not proven successful in practice. One is the need to limit the balloon wall thickness and the need to maintain balloon wall flexibility to facilitate access to, and withdrawal from, a bone cavity.
In treating a vertebral fracture, for example, the vertebral cavity is typically accessed by drilling a small hole and locating a short, hollow, metallic tubular element (canula) through the left or right pedicle portion (or sometimes both) of the vertebral arch (see, e.g., FIG. 2 of U.S. Pat. No. 5,972,015, which shows the left and right pedicle portions 42 of vertebral arch 40, and FIG. 6 of the same patent which shows an access hole for catheter tube 50 and expandable structure 56 through one pedicle portion 42 into the interior volume 30 of reticulated cancellous, or spongy, bone 32). Because pedicle portion 42 shown in FIGS. 2 and 6 of the Scribner '015 patent is relatively small and is itself readily susceptible to fracture if its structural integrity is impaired by too large a hole, it is crucial to keep the diameter of the hole, therefore also of the canula, to a minimum, typically no larger than about 4-5 mm. The canula helps to protect surrounding bone portions from abrasion and from expansion forces while inserting or removing the catheter shaft or while inflating the balloon element.
Thus, conventional practice has been to fold or wrap the balloon-like element relatively tightly around the end of a catheter shaft in order to keep the maximum diameter of the unit at the balloon end small enough to fit through the canula of a small-diameter pedicle hole. If a balloon-like expandable element was fabricated having relatively thick walls and/or made from a relatively stiff, less flexible material, such an element might well be inflatable to a higher pressure, but it generally could not be wound tightly enough about the distal end of a catheter shaft to fit through a narrow-diameter pedicle hole.
Even assuming that it were possible somehow to wrap a relatively thick-walled and/or stiff balloon element sufficiently tightly to facilitate insertion of the device through a narrow-diameter pedicle hole, it then would be virtually impossible using prior art technology to remove or withdraw the balloon element through the same hole or canula following dilatation. The reason is that, after a cycle of inflation and deflation inside the vertebral cavity, a thick-walled/relatively inflexible balloon element cannot be refolded or rewrapped in-situ to a sufficiently small diameter to be capable of being withdrawn through the canula without the use of excessive force which might crack or break the pedicle.
In another example, a balloon catheter according to the present invention can be used to treat congenital obstructions of the nasal lacrimal duct. This procedure requires inserting an inflatable element at the distal end of a catheter through the very narrow and sensitive lacrimal duct, inflating the balloon to compress the obstruction and open the passageway, deflating the balloon, and thereafter removing the deflated balloon element through the lacrimal duct. Following inflation, however, the balloon element may not return to its pre-inflation profile making withdrawal difficult.
These and other deficiencies in and limitations of the prior art approaches to treating bone deformities, such as vertebral body compression fractures, and other medical treatments involving inserting, inflating, and thereafter deflating and removing a balloon element through a relatively narrow body passageway are largely if not completely overcome with the apparatus and methods of this invention for bone, tissue and duct dilatation.